The present application relates to antennas, and more particularly, but not exclusively, relates to the increasing the bandwidth of an electrically small antenna. In one nonexclusive application, this antenna technology finds application in wireless communications. As used herein, the term “electrically small” when used to describe an antenna refers to an antenna with a maximum dimension less than one-half the wavelength of its operating frequency.
Electrically small antennas present operating challenges in the current art and commonly are considered to perform poorly. An antenna performs most efficiently when the maximum power is transferred to the antenna (for a transmitter) or from the antenna (for a receiver) for a given power input. To maximize power transfer, it is often desirable to closely match input impedance of the antenna to the characteristic impedance of the power line operatively coupled thereto. Maximum power transfer can occur when the real part of the matched impedances have the same magnitude (the resistances), and when the imaginary parts (the reactances) have the same magnitude and are of opposite signs, such that they are 180 degrees out of phase with one another. Because the impedances of low-loss transmission lines are nearly real, it is often the case that an antenna is most effective when near self-resonance, where the antenna input reactance is nearly zero. The input impedance of an electrically small antenna can be difficult to match because the radiation from a small transmitting antenna is inversely related to the antenna size in wavelengths, whence the antenna reactance is small as also is the antenna resistance.
Antennas that are physically small compared to wavelength have input impedances with relatively large reactance values except near the resonance frequency. At resonance, the input reactance tends to diminish and the input resistance is usually small. Therefore, electrically small antennas typically demonstrate relatively small match bandwidth.
Consumers are typically interested in electronic devices that are smaller and more efficient in power usage, allowing longer use and battery life. Additionally or alternatively, it is often desirable to increase the bandwidth of communication devices such as mobile phones, GPS devices, radios, and the like. The space occupied by an antenna relative to its effectiveness is often of interest in relation to such equipment. Thus, there is a need for further contributions in this area of technology.